Oh, absolutely - this would be if I didn't want a straight-up clean boost but wanted to mis-bias the added gain stage for effect. For instance, there's a fuzz called the Baron Samedi which tacks a transistor-based boost at the end of a Bosstone, and by changing that third transistor's bias you can get some very interesting sounds.You could mess with the resistors in the voltage divider that establish vref but why would you? Maximum headroom and stability will be achieved by biasing to vref.
Well, vref will usually be 1/2 vcc. There's no schematic, but I'm guessing the two 1M resistors form the voltage divider that sets vref to 1/2 vcc. Change one of the resistors to another value and the reference voltage will be offset from the usual 1/2 vcc. This would allow the op amp to swing asymmetrically and also clip asymmetrically. This may or may not sound good.Oh, absolutely - this would be if I didn't want a straight-up clean boost but wanted to mis-bias the added gain stage for effect. For instance, there's a fuzz called the Baron Samedi which tacks a transistor-based boost at the end of a Bosstone, and by changing that third transistor's bias you can get some very interesting sounds.
I'm not certain this can be done with an IC, but would love to know!
That would rule the school, of course! I recently made a stripboard Boss T-Bone and it's the size of a postage stamp, so... it can go anywhere!If you want a fuzz on a 3PDT board we can make that happen....
Yep I was looking at those 1M resistors... hmm. Just don't know how that kinda thing works with ICs.Well, vref will usually be 1/2 vcc. There's no schematic, but I'm guessing the two 1M resistors form the voltage divider that sets vref to 1/2 vcc. Change one of the resistors to another value and the reference voltage will be offset from the usual 1/2 vcc. This would allow the op amp to swing asymmetrically and also clip asymmetrically. This may or may not sound good.
When you drive an op amp beyond its output swing range, 0V to 9V for example, the output signal will start to clip. More gain = more clipping. Less supply voltage = earlier clipping. You bias to 1/2 VCC, 4.5V in this case, to ensure the output can swing symmetrically around this midpoint because it will maximize the available range and thus clean headroom. When you intentionally misbias the op amp, the output will swing asymmetrically, meaning one side of the output signal will hit the power rails sooner than the other and thus also clip sooner. This will create asymmetrical distortion.Yep I was looking at those 1M resistors... hmm. Just don't know how that kinda thing works with ICs.
Gotcha, thanks for the clarification. I kinda figured it wouldn't be a worthwhile experiment in the way it can be with BJTs.When you drive an op amp beyond its output swing range, 0V to 9V for example, the output signal will start to clip. More gain = more clipping. Less supply voltage = earlier clipping. You bias to 1/2 VCC, 4.5V in this case, to ensure the output can swing symmetrically around this midpoint because it will maximize the available range and thus clean headroom. When you intentionally misbias the op amp, the output will swing asymmetrically, meaning one side of the output signal will hit the power rails sooner than the other and thus also clip sooner. This will create asymmetrical distortion.
You should be aware, op amp clipping is kind of an aquired taste and doesn't always sound very nice unless the circuit is really built around it. That's not going to change much by misbiasing the op amp either.
After all, this isn't really a board to experiment with - it's to bring those pesky FY-2's and Big Cheeses past unity!![]()
Ha, nice! Yep those are a couple main offenders I can think of, I'm sure there are others...I am reading this post, halfway though go to the store and add on to my care for my FY-2!
Gotcha, thanks for the clarification. I kinda figured it wouldn't be a worthwhile experiment in the way it can be with BJTs.
After all, this isn't really a board to experiment with - it's to bring those pesky FY-2's and Big Cheeses past unity!![]()
For the nonsense I'm talking about, @Feral Feline had an a idea to convert one of those GPCB AfterBlasters from JFET to BJT, but I haven't tried it yet...